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EFFECT OF CHEMICAL IDENTITY AND MORPHOLOGY ON AMPHIPHILIC-ZWITTERIONIC BLOCK COPOLYMER MEMBRANES
Author ORCID Identifier
Open Access Dissertation
Doctor of Philosophy (PhD)
Polymer Science and Engineering
Year Degree Awarded
Month Degree Awarded
Dr. E. Bryan Coughlin
Membrane Science | Polymer and Organic Materials | Polymer Chemistry | Polymer Science
Amphiphilic block copolymers have gained a broad research interest attributed to their self-assembly properties over a range of pH, temperature, and ionic strength. Polyzwitterions have attracted special attention due to their hydrophilicity, charge sensitivity and coulombic attraction of the opposite charges over a range of environments making them a popular material of study in the field of stimuli responsive systems, for example in self-healing hydrogels, and water transport membranes. Combining the stimuli responsiveness and higher hydrophilicity of zwitterionic polymers with self-assembly behavior of amphiphilic block copolymers created an interest to study the effect of composition and identity of the zwitterionic block on the morphology of novel amphiphilic- zwitterionic block copolymer systems.
A novel chemistry to synthesis a series of amphiphilic-zwitterionic block copolymer was developed. As a first step, a parent block copolymer precursors of poly (dimethyl amino ethyl methacrylate)-b-poly (n butyl acrylate-ran-allyl methacrylate) (PDMAEMA-b- P(nBA-ran-AMA)) with different copolymer volume fractions were synthesized using controlled radical polymerization. The advantage of using this technique is the ability to synthesize a polymer chain with predetermined molecular weight and well-defined chemical composition while also maintaining a narrow dispersity. Variation of the zwitterionic groups; sulfobetaine, carboxybetaine or cholinephosphate were investigated through post-polymerization modification of the PDMAEMA block using nucleophilic ring-opening reactions of 1,3-propane sultone , β-propiolactone or n-butyl substituted phospholane. Proton NMR spectroscopy data were analyzed to calculate degree of polymerization (DP) from the distinct peak of each repeating unit of pendent groups in parent neutral block copolymers and its modified amphiphilic-zwitterionic counterpart. These DP of the neutral block copolymer were then used to calculate the relative volume fraction of each block and aid the future calculation of post-polymerization modification on the PDMAEMA block and crosslinking chemistry on the poly allyl methacrylate (PAMA) block. Thermal stability of these zwitterionic systems was investigated by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).
Mechanically robust free standing amphiphilic zwitterionic copolymer poly (n butyl acrylate-ran-allyl methacrylate)-b-polybetaine methacrylate membrane were tailored using thiol-ene click chemistry on the pendent double bond of the allyl methacrylate repeating unit with a dithiol crosslinking agent under UV irradiation. The analysis of the effect of composition, and identity of the zwitterionic block on the resultant films ix morphologies was probed. The systematic variations in volume fractions of each block were targeted to generate different morphologies. The impact of the copolymer composition on the morphology were analyzed using small angle X-ray scattering (SAXS). Various relative humidity sweeps and temperature variation SAXS were performed through collaboration with Argonne National Laboratory to investigate the effect of different environmental conditions of the morphologies. In addition to SAXS, transmission electron microscopy (TEM) was performed to study real space imaging of these structures. With the results from these characterization methods, it was possible to perform a structure-property relationship study of these novel Amphiphilic-Zwitterionic block copolymers.
Looking forward, results from this study have the potential to guide future applications in the field of water transport filtration membranes. The effect on morphology, zwitterionic content and block copolymer composition on water uptake and salt uptake was evaluated using gravimetric analysis, and dead-end filtration performance studies showing promising initial results.
"EFFECT OF CHEMICAL IDENTITY AND MORPHOLOGY ON AMPHIPHILIC-ZWITTERIONIC BLOCK COPOLYMER MEMBRANES" (2023). Doctoral Dissertations. 2745.
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